The National Security Agency sometimes amasses so much data from email contact lists that it occasionally has to stop collection to weed out unneeded intelligence, according to documents leaked by Edward Snowden to the Washington Post.

The report published on Monday shows that the NSA collects contact lists from popular messaging services – including those run by Google, Facebook, Microsoft and Yahoo – without court approval. The intelligence agency can do this because it pulls the data from non-U.S. data centers run by major Internet companies. (The NSA has secret relationships with foreign Internet providers and intelligence agencies that control facilities used to direct data as it travels the Internet, the Post reported.) Although that still allows the U.S. government to collect address book information on millions American Web users, it complies with the law because the effort is targeted at foreigners, according to the Post.

But mining contact lists – which include email addresses, phone numbers and physical street addresses – sometimes threatens to provide more data than the NSA can handle.

According to the Post:

During a single day last year, the NSA’s Special Source Operations branch collected 444,743 e-mail address books from Yahoo, 105,068 from Hotmail, 82,857 from Facebook, 33,697 from Gmail and 22,881 from unspecified other providers, according to an internal NSA PowerPoint presentation. Those figures, described as a typical daily intake in the document, correspond to a rate of more than 250 million per year.

Internet companies often transmit contact list data each time a user logs on.

When it get overwhelmed with data, the agency then stops collection under an “emergency detasking” order to narrow the scope of its inquiry, according to the Post. In an undated presentation, the NSA’s Special Source Operations unit tells analysts to be more selective in collecting data because of the challenge of keeping it all. “Memorialize what you need,” the slide suggests, rather than “order one of everything off the menu and eat what you want.”

In an email, an NSA spokeswoman said the agency “is focused on discovering and developing intelligence about valid foreign intelligence targets like terrorists, human traffickers and drug smugglers,” an NSA spokeswoman said in an email.

Because the reported collection occurs overseas, the NSA does not need to notify companies.

“We have neither knowledge of nor participation in this mass collection of webmail addresses or chat lists by the government,” a Google spokeswoman said.

Microsoft spokeswoman Nicole Miller referred a reporter to her comment in the Post story. The company “does not provide any government with direct or unfettered access to our customers’ data,” she told the Post.

Facebook and Yahoo did not immediately respond to requests for comment.

This post has been updated to include more details about how the NSA program collected data overseas.